1. Field of the Invention
The present invention relates to a developing roller to be used in an electrophotographic image forming apparatus, such as a copying machine and a laser printer, and an electrophotographic process cartridge and an electrophotographic image forming apparatus which are provided with the developing roller.
2. Description of the Related Art
As a development method of visualizing an electrostatic latent image existing on the photosensitive drum with the use of the toner, a contact development method in which a developing roller carrying a toner is brought into contact with a photosensitive drum is known. The developing roller is required to have a function of imparting an adequate frictional charge to the toner. In the contact development method, a negatively chargeable one-component developer is generally used in many cases. In two such examples, Japanese Patent Application Laid-Open No. 2000-181218 and Japanese Patent Application Laid-Open No. 2003-122108 disclose a developing roller which uses a resin coating layer containing nitrogen in the surface layer of the developing roller, as a developing roller which can efficiently impart a high electric charge to a negatively chargeable toner.
In addition, a developing roller provided with an elastic layer is proposed in order to secure a nip width on a contacting portion with the photosensitive drum. However, in the developing roller having the elastic layer, a low-molecular-weight substance, which is unavoidably contained in the elastic layer, occasionally bleeds out to the surface. The low-molecular-weight substance having bled out adheres to the surface of the photosensitive drum, which is in contact with the developing roller, and thereby occasionally affects the quality of the electrophotographic image and the life of the photosensitive drum. As a result, Japanese Patent Application Laid-Open No. 2005-215485 discloses a developer-carrying body provided with a shielding layer which shields a bleeding material that bleeds from the elastic layer.